1. Technical Field
The present invention relates to a non-aqueous secondary battery, and particularly, a negative electrode material for the non-aqueous secondary battery.
2. Prior Art
In recent years, the miniaturization and lightening of portable devices have been remarkable, and with this tendency, the miniaturization and lightening of the batteries which can be used as power sources of the portable devices have been required very strongly. In consequence, various non-aqueous secondary batteries such as the so-called lithium battery have been suggested.
In the lithium battery, it is desirable to use metal lithium as a negative electrode. However, particularly in the case that the lithium battery is used as the secondary battery, an irreversible change of lithium such as the production of dendrite-like lithium occurs by the repetition of charge and discharge, so that problems such as capacity loss and safety decrease take place. Thus, satisfactory results have not been obtained so far.
Hence, one usual strategy for solving these problems is to use a carbon material as the negative electrode. As the carbon materials, graphite (JP-A-62-23433), pitch cokes (e.g., JP-A-62-122066 and JP-A-2-66856) and the like have been suggested.
In the carbon materials, however, it is difficult to exceed a theoretical capacity of graphite (372 mAh/g), and hence various amorphous carbons have been suggested. In the cases of these amorphous carbons, a high capacity can be obtained only in a cycle of charging and discharging at a low current, (e.g., approximately 0.1 mA/cm.sup.2), but under actual use conditions, a low capacity (&lt;270 mAh/g) can merely be obtained. The further improvement of the performance have been desired.